1. Field of the Invention
The instant disclosure pertains to thermostable DNA polymerases which exhibit improved robustness and efficiency. In particular, the DNA polymerases have been shown to result in a substantial improvements in desirable properties as compared to the native DNA polymerases when used in DNA sequencing reactions.
2. Background
DNA polymerases are enzymes which are useful in many recombinant DNA techniques such as nucleic acid amplification by the polymerase chain reaction (“PCR”), self-sustained sequence replication (“3 SR”), and DNA sequencing. Thermostable DNA polymerases are particularly useful. Because heat does not destroy the polymerase activity, there is no need to add additional polymerase after every denaturation step.
Naturally occurring DNA polymerases preferentially incorporate unlabeled nucleotides over corresponding labeled nucleotides into polynucleotides. This ability of DNA polymerases to discriminate against fluorescently labeled nucleotides had an undesirable effect on many molecular biology procedures that require the enzymatic addition of labeled nucleotides, e.g., labeled dideoxy terminator sequencing. Ambiguous sequencing determinations often result from the disproportionate number of labeled and unlabeled dideoxy terminators and nucleotides. On an electropherogram obtained from a capillary electrophoresis sequencing unit, this phenomena shows up as uneven peaks. Large signals due to a larger amount of incorporated labeled ddNTP can obscure smaller signals and lead to ambiguous sequence determinations. Additionally, many of the enzymes presently available are sensitive to high salt environments.
Thus, a need continues to exist for an improved DNA polymerase having improved discrimination properties (and thus resulting in improved signal uniformity) and increased tolerance to high salt conditions. These and other concerns are addressed in greater detail below.